Tap changer



Aug 6, 1968 G. A. WILSON, IR 3,396,248

TAP CHANGER Filed Dec. 12, 1966 ,2 4 Sheets-Sheet l Aug. 6, 1968 Filed Dec.

G. A. WILSON, JR

TAP CHANGER 4 Sheets-Sheet 2 L7/MM' dwarf/ey Aug- 6, 1968 G. A. WILSON, JR 3,396,248

TAP CHANGER Filed Dec. 12. 1966 4 Sheets-Sheet 3 Aug' 6, 1968 G. A. WILSON, JR 3,396,248

TAP CHANGER Filed Dec. l2, 1966 4 Sheets-Sheet 4 M aw/ry United States Patent 3,396,248 TAP CHANGER Gordon A. Wilson, Jr., Washington, Pa., assignor to McGraw-Edison Company, Elgin, Ill., a corporation of Delaware Filed Dec. 12, 1966, Ser. No. 600,950 Claims. (Cl. 200-11) ABSTRACT 0F THE DISCLOSURE A tap changer is provided which includes a coarse switching assembly for achieving adjustment in relatively wide range Voltage steps and a Vernier switching assembly for achieving adjustment in relatively narrower range Voltage steps within each of the wide range Voltage steps. A common drive is disclosed for both the coarse and Vernier switching assemblies.

This invention relates to switching mechanisms and, more particularly, to load tap changing mechanisms of the type commonly used for example in connection with stationary induction apparatus.

Tap changers of various design are well known in the electrical industry. Conventional tap changing mechanisms generally adjust Voltage in rather wide voltage increments. For most installations such voltage adjustment is not critical or detrimental but in some applications the wide Voltage adjustment cannot be tolerated. In those applications where wise voltage adjustments cannot be tolerated auxiliary equipment is used to smooth out the relatively large voltage Variations. For example, saturable reactors have been used to insure that the apparatus being supplied with electrical power through the induction apparatus is not subjected to sudden, large changes in voltage.

An example of an application wherein large voltage variations must be avoided is in the chemical industry in connection with Various electrolytic processes which are carried out using electrical energy supplied through a rectifier system. The rectifier system is supplied with electrical energy through stationary induction apparatus, a regulator, having a tap changer which regulates the supply voltage. Due to the nature of the electrolytic processes, they are susceptible to electrical changes as the process progresses. For example, bubbling in the area of the electrodes can produce changes in voltage and amperage. These changes are reflected in the tap changer which operates to adjust the tap connection, or connections, to accommodate the voltage changes. With conventional tap changers the Voltage adjustment which occurs to compensate for Voltage changes are relatively large and subject the rectiiier system to abrupt, wide Voltage changes. Rectifiers, particularly those of solid-state or semi-solid-state construction cannot tolerate such voltage changes and will fail under such conditions. As stated above, one proposal for correcting this situation in the past has been the use of saturable reactors in combination with the induction apparatus in an effort to smooth out the Voltage changes. Such proposals are not satisfactory as they increase equipment costs and are not an efficient use of available electrical power. It will be appreciated that this discussion of an electrolytic process is given merely as an example and should not be construed as a limitation on the possible scope of use of this invention.

A general object of this invention is to reduce the magnitude of voltage changes which occur in the operation of a tap changer.

A more specific object of this invention is to provide a tap changer which achieves Voltage adjustment in two ranges of adjustment; namely, in relatively wide voltage ICC range steps (coarse adjustment) and, within each such wide step, in narrower range voltage steps (Vernier adjustment).

A further object of this invention is to simplify the construction and control of tap changers having such dual range adjustment.

A more speciiic object is to provide a tap changer which can be used effectively in applications which cannot tolerate abrupt, wide changes in voltage.

For the achievement of these and other objects, this invention contemplates a tap changer having both a coarse switching assembly and a Vernier switching assembly, the latter being capable of operating within the steps of Voltage adjustment of the coarse switching assembly to thereby achieve precise voltage adjustment gradually and smoothly. Moreover, the tap changer constructed in accordance with this invention preferably utilizes a common drive for both the coarse and Vernier switching assemblies. The common drive is preferred over a dual drive mechanism for example, as it is easier to control and coordinate for more eiTectiVe switching 4operation and also results in a simpler and more compact assembly.

Other Iobjects and advantages will be pointed out in, or be apparent from, the specification and claims, as will obvious modications of the embodiment shown in the drawings, in which:

FIG. 1 is a front elevation of coarse and Vernier switching assemblies constructed in accordance with this invention;

FIG. 2 is a section View taken generally along line 2-2 of FIG. 1;

FIG. 3 is a section View taken generally along line 3 3 of FIG. 1;

FIG. 4 is a front elevation of the drive unit;

FIG. 5 is a section View taken generally along line 5 5 of FIG. 4;

FIG. 6 is a partial rear elevation of the drive unit;

FIG. 7 is a schematic drawing of a portion of the circuit controlled by the tap changer illustrated in the drawings; and

FIG. 8 is a partial View illustrating movement of the movable coarse contact assembly.

This invention is illustrated in the drawings as incorporated in a three-phase load tap changing regulator. The switching assembly ofthe load tap changing mechanism is generally located in a Sealed, oil iilled compartment. Only the rear wall portion 10 of the compartment is illustrated, the rear wall being attached directly to the outer transformer tank wall. A drive unit 12 for the switching assembly is positioned below the switching assembly compartment and consists of a suitable drive mechanism, to be described hereinafter, located within a weatherproof enclosure. The tap changing switch mechanism of this invention is adapted to provide both coarse and Vernier adjustment with a coarse switching assembly 14 and a Vernier switching assembly 16 being lprovided for each phase. For purposes of illustration, portions of both the coarse and Vernier switching assemblies in the Various phase positions have been removed and for convenience reference will be made to the coarse and Vernier switching assemblies as though only one of each were illustrated, it being understood that the description is applicable to all ofthe switching assemblies.

The coarse switching assemblies are mounted on a panel 18, of electrical insulating material, and the Vernier switching assemblies are mounted on a separate panel 20 also of electrical insulating material. These insulating panels are positioned at openings 22 and 24 in the transformer tank wall and each panel has a sealing engagement with the tank Wall at its respective tank opening.

Turning rst to the Vernier switching assemblies, FIGS. l and 2, each such assembly includes nine angularly spaced stationary contacts 26, for convenience the contacts are shown schematically in the left phase of FIG. 1 and only two are shown in more detail in the center phase. The stationary contacts include a iirst set of nine co-planar metallic contacts 26a disposed in a circle and spaced axially from a second set of nine co-planar metallic contacts 26b also arranged in a circle. The spaced metallic contacts are supported in pairs on threaded studs 28 and are held in spaced relation by a metallic sleeve 30. Stud 28 is anchored in a contact support 32 which is rigid with threaded pin 34 extending through an opening in panel 20. An insulating collar 36 spaces support 32 from the panel and, together with a second collar 38, insures a seal at the opening in the panel. Nut 40 secures the stationary contact assembly to the panel 20 and the inner end of pin 34, i.e. that which extends into the transformer tank, is provided with suitable terminal attachments 42 to function as a terminal point for an electrical lead (not shown) through which connection is made to a tap in regulator winding.

An autotransformer type winding arrangement is used, for example eight of the stationary contacts are connected to individual taps (see FIG. 7) in a tapped Vernier series winding 44 of the corresponding phase of the transformer and the ninth contact serves as a neutral contact for the winding. In FIG. 7 the tap connections in winding 44 are designated as N and 2-9. For convenience, the stationary contacts have not been illustrated in FIG. 7 but it will be appreciated that they are positioned electrically between the tap connections N and 2 9 and the movable contacts of the switch assembly as will be described more completely hereinafter.

Insulating panel board 46 is also disposed within the oil lled compartment, and is supported in spaced relatioriship from panel 20 by electrical insulating Sleeve assemblies 48. Structurally sleeve 50 of electrical insulating material extends from panel 20 to panel 46 and a threaded stud 52 is utilized to bolt panel 46 in fixed relationship to panel 20.

A rotatable shaft 54 carries a movable contact 56 for sequential engagement with stationary metallic contacts 26b. Structurally, shaft 54 extends through an opening in panel 46 and is mounted with its axis coincident with the axis about which stationary contacts 26 are spaced. One end of shaft 54 is journaled at 57 in bracket 58 which is secured to panel 46. Switch arm is attached to shaft 54 and carries movable contact 56. Structurally contact 56 includes a pair of oppositely arranged laminated conductive shunts 62. Each shunt 62 has a contact button 64 at its inner radial end and an arcing contact button 66 at its outer radial end. In a conventional manner shunts 62 are connected for swivel movement about pins 68 which are supported in a thrust member 70. Arcing contact buttons 66 are arranged in opposed relationship and are urged toward each other by compression springs 72 mounted on through pin 74. Similarly, inner contact buttons 64 are in opposed relationship and are urged toward each other by compression springs 76 mounted on pin 78. With this arrangement the laminated shunts are urged toward engagement with thrust member and the contact buttons 66 are urged into engagement with opposite sides of metallic contacts 2Gb. A collector ring 80, made of suitable conductive material, is tixed to panel 20. A radial ange 82 of the collector ring is preferably cot-planar and co-axial with metallic contact 26b. Collector ring 80 is suitably connected to panel 20 by -pin 84 and nut 85 and provides a terminal 86 for a conventional connection of the collector ring within the transformer tank and to the transformer assembly, specically to one of load terminals L1, L2 and L3 (see FIG. 7) in a conventional manner. A second movable contact 88, identica-l in construction to contact 56, is connected through arm 90 to sleeve 92 surrounding and rotatable with respect to shaft 54. Movable contact 88 is arranged to `bridge between selective ones of metallic contacts 26a and a second collector ring 94. Collector ring 94 is supported on panel 46 and is connected electrically to conductive strap 98. Conductive strap 98 terminates at terminal 100 from which a suitable electrical connection is made to load terminals L1, L2 and L3. Preferably the electrical connections of the collector rings to the load terminals are made 4through preventive autotransformers as illustrated schematically in FIG. 7.

Since metallic contacts 26a and 26h are electrically common through conductive sleeve 30, rotatable contacts 56 and 88 can be indexed to a bridging position where one of the rotatable contacts 56 or 88 is engaged on one of two adjacent stationary Contacts 26 and the Voltage obtained is midway between the two taps, .or the movable contacts can be indexed to a symmetrical position Wherein both are engaged to the same stationary contact.

Movement of rotatable contacts 56 and 88 with respect to the stationary contacts is achieved through a drive mechanism 102. The drive mechanism consists of a scroll cam 104 and a pair of spaced index plates 106 and 108. Each of the index plates carries a series of rollers and 112 which are arranged for selective engagement in the track 114 of the scroll cam. Plate 106 is rotatable with sleeve 92 and index plate 108 is fixed to and rotatable with shaft 54 to selectively drive one or the other of the rotatable contacts. Upon each 180 of rotation of scroll cam 104, one of the indexing plates is rotated to displace its respective movable contact while the other indexing plate is held in position by the scroll cam. As the scroll cam rotates one movable contact is driven from one stationary contact to a succeeding contact while the dwell portion of the cam holds the other stationary contact in engagement with the preceding stationary contact. Thus only one contact moves for each 180 of rotation of scroll cam 104 and two such increments of scroll cam rotation are required to effect movement of both movable contacts to a succeeding stationary contact.

The construction and operation of the Vernier switching mechanism described to this point is described and claimed in Gordon A. Wilson, Jr., Patent No. 3,155,782, issued Nov. 3, 1964, and assigned to the assignee of this application. The description made herein is believed to be sucient for an understanding of the present invention and reliance is placed on the aforementioned patent for a more complete description of the mechanical arrangement and electrical operation of the contact assemblies and the scroll cam drive of the Vernier switching assembly.

As stated hereinabove, each of the Vernier switching assemblies are identical both in construction and operation. The scroll cams for each of the Vernier switching assemblies are mounted on rotatable shafts 116, 118 and 120. The shafts are suitably supported in brackets 58 and are interconnected for joint movement by couplings 122 and 124. The actual connection between the couplings and the shafts can take any conventional form.

Turing to the coarse switching assemblies of the tap changer, switching assemblies 14 are all structurally identical and again portions of each assembly at the various phases have been removed for illustrative purposes and the coarse switch assemblies will be disclosed as one. Each coarse switching assembly is provided with nine stationary contact assemblies 130. These stationary contact assemblies are structurally similar to stationary contacts 26 of the Vernier switching assembly with one exception which will be discussed. More specifically, each stationary contact includes a first set of nin-e angularly spaced co-planar stationary metallic contacts a and a second set of nine angularly spaced co-planar stationary contact members 130b which are spaced axially from members 130a. The stationary contact members are electrically connected by a metallic sleeve 132, the sleeve and stationary contact portions 130a and 130b being supported on a threaded bolt 134. Bolt 134 is connected through support 135 to a threaded pin 137 which projects into the transformer interior for connection to the tapped series coarse winding 139 (see FIG. 7) through suitable leads (not shown). Again an autotransformer arrangement is used and the tap connections in winding 139 have been identified as A-H and J but stationary contacts 130 have not been shown in FIG. 7. Stationary contacts A and J differ from the remaining contacts in that, at A rear contact 130b has a lesser arcuate extension than 130a and at I the 130a has a less arcuate extension; otherwise the remaining contacts 13011 and 130b have the same extension as 130:1 at A.

A rotatable contact assembly 140 is arranged for engagement with metallic contacts 130b and includes a pair of shunt bars 142, 144 having buttons 146 and 148 provided on the outer radial ends thereof to engage opposite surfaces of metallic contacts 130k. The inner radial ends of the shunt bars carry contact buttons 150 and 152 which engage a radial fiange 154 of a conductive collector ring 156. The radial flange is co-axial and co-planar with metallic contacts 130b. Support plate 158 is disposed between shunt bars 142 and 144 and is bolted to the free end of radial arm 160. A spring and pin assembly includes pins 166 which extend through shunt bars 142 and 144 and support plate 158 and compression springs 168 which are seated between caps 170 or shoul-ders 171 and the outer faces of the shunt bars. The springs bias the shunt bars, and contact buttons, toward each other and into engagement with metallic contacts 130b and radial flange 154. In this manner selective electrical connection is made between stationary contacts 130 and collector ring 156.

Arm 160 is connected to the end of shaft 162 which extends through front plate 164 and has its opposite end suitably journaled in bracket 167. Bracket 167 is generally U-shaped and is fixed to plate 164. Shaft 162 has a splined end 169 which has a driving connection with Geneva gear 172. Rotation of the Geneva gear is transmitted through shaft 162 and arm 1-60 to contact assembly 140 to move that assembly relative to the stationary contacts.

Plate 164 is supported from panel 18 by a plurality of support posts 173. The support posts comprise a threaded stud 174 which extends through panel 18 and plate 164 and carries an insulating sleeve 176 to maintain spaced relationship between panel 18 and plate 164. Inner end 178 of stud 174 also provides a terminal as will be discussed more completely hereinafter.

A second rotatable contact assembly 190 is arranged for selective engagement with stationary metallic contacts 130a. The structure of contacts 190 is identical to that of contacts 140 and therefore will not be described in detail and Where necessary the same numerals will be used to identify corresponding elements. In movable contact assembly 190, support bar 158 is connected to a radial arm 192 which is in turn connected to a sleeve shaft 194. Shaft 194 is carried on and is rotatable with respect to shaft 162. End 196 of the shaft is splined to establish a driving connection between that shaft and a second Geneva gear 198. In this manner rotation of Geneva gear 198 is transmitted through shaft 194 and arm 192 to move rotatable contacts 190 with respect to stationary contact members 130g. In this instance contact buttons 150 and 152 of rotatable contact 190 engage radial flange 200 of collector ring 202. Collector ring 202 is fixed to plate 164 by bolts 204. The electrical connection between the coarse and Vernier windings is illustrated schematically in FIG. 7. Structurally, rotatable contact 190 is connected to one side of Vernier winding 44 through collector ring 202, which has a suitable electrical connection (not shown) to bus bar 191 attached to terminal 178, and through bus bar 191 to one end of the winding. The other end of the winding is connected through terminal 193 of collector ring 156 and the collector ring to movable contact assembly 140. In this manner the Vernier winding can be selectively connected to the tap connections in the coarse winding.

Each of the Geneva gears is provided with a set of nine angularly spaced, conventional Geneva teeth 206. Each Geneva gear is associated with a separate Geneva pinion and stop 208 and 210. Geneva pinion 208 is of conventional construction having a body portion 212, arm portions 214 and 216 extending on opposite sides of Geneva gear 172 and supporting a Geneva pin 218 therebetween, the Geneva pin adapted to be selectively engaged in the radial slots provided between the Geneva teeth. The portion -of body 212 between arms 214 and 216 is cut away to provide clearance for the Geneva teeth whereas the opposite side 220 of each Geneva pinion is circular for engagement in the concave indentation 222 of the Geneva teeth to provide a stop. Similarly, Geneva pinion 210 includes a body porti-on 224 and radial arms 226 and 228 carrying a pin 230 for selective engagement with the radial slots between the teeth of Geneva gear 198. Also clearance for the teeth is provided between the radial arms and the outer free end 232 of the Geneva pinion is circular to engage the concave portion 223 of the Geneva teeth 207. Geneva pinions 208 and 210 have a splined connection with shaft 234 and rotate simultaneously in response to rotation of shaft 234. One end of shaft 234 is journaled in a suitable bushing 236 pnovided in plate 164 -and the opposite end of the shaft passes through a support bracket 238 and has a splined connection with bevel gear 240. Bracket 238 is fixed to plate 164 and carries a suitable bushing 242 to provide a bearing for shaft 234.

In order to achieve the desired coarse and Vernier tap changes this invention proposes a drive system which is effective to establish a coarse voltage setting and then continue with Vernier adjustment without disturbing the coarse voltage setting. In the illustrated embodiment the coarse switching -assembly is stepped by its Geneva drive until it achieves the coarse adjustment in the tap changer and, after the coarse adjustment is selected, the Vernier switching assembly is actuated within the coarse adjustment to achieve the desired voltage setting. In the preferred embodiment a Geneva drive is used in the coarse switching assembly as this provides a simplified drive arrangement and to further simplify the drive arrangement the Geneva pinions are driven from the same shaft. In the preferred embodiment, the Geneva gears are offset and the Geneva drive pinions are offset 40 from each other (see FIG. l). In FIG. 1 rotatable contacts and 190 and Geneva pinions 208 and 210 are illustrated in an initial setting of the coarse switching assembly. To achieve coarse ladjustment from that initial setting the contacts are moved counterclockwise to a given position and at that point the Geneva stop arrangement holds the coarse switching assembly in that position while the scroll cam and index plates of the Vernier switching arrangement are available for operation to provide further Voltage adjustment by changing its tap connections. The specific operation of the coarse and Vernier switching mechanisms will be described more completely hereinafter.

It will be appreciated that switch assembly drives other than the scroll cam and Geneva gear arrangements could be used. The Geneva gear and pinion arrangement is preferred as it provides a relatively simple and effective manner of providing coarse adjustment `and then holding a coarse -adjustment during operation of the Vernier switching mechanism. The load tap changing mechanism of this invention provides an even further simplification in mechanical structure by utilizing a common drive source for the separate coarse and Vernier switching assembly drives. With a common drive source balancing and/ or synchronization of the drive for the Vernier and coarse adjusters is achieved more readily. More particularly, an output shaft assembly 252 extends from drive unit 12 and through a spring loaded stuffing box 256 of conventional construction connects to a universal drive shaft assembly 254 in the tap changer compartment. The

stufling box provides a sealed point of entry for the drive train through the normally oil filled compartment. Structurally drive shaft assembly 254 comprises a coupling 262 between the shaft extension of the stuffing box 256, and shaft 260 and a coupling 272 between shaft 260 and shaft 258. Shaft section 260 is supported for rotation in bearings 264 and 266 mounted in brackets 268 and 270 extending from plate 164. Shaft section 262 has a driving connection with a second drive shaft section 272 which is supported at its opposite end in an L-sh-aped bracket 274.

The take-off of rotational movement from drive shaft assembly 254 to the coarse switching assemblies is accomplished through a set of bevel gears 276 and 278. Gear 276 is connected to drive shaft section 260 and gear 278 has a spline connection to shaft 245. Shaft 245 is supported for rotati-on in bushing assemblies 248 mounted in bracket arms 244 and 246. Bevel gear 250 has a spline connection with shaft 245 and engages bevel gear 240. In this manner rotation is transmitted from drive shaft assembly 254 to bevel gear 240 to drive the Geneva pinions. Each of the coarse switching assemblies includes a bevel gear 240 connected to drive the Geneva pinions of the switching assemblies. The drive arrangement for each bevel gear 240 is identical, bevel gears 250 are connected to shafts 245 supported in arms 244 and 246 and the bevel gears engage Geneva pinion drive gears 240. Shafts 245 are connected for joint movement by couplings 243.

The take-olir of rotational movement from drive shaft assembly 254 to the Vernier switching assemblies is made through miter gears 280 and 282. Miter gear 280 is connected to drive shaft section 272 and gear 282 is connected to shaft 116 which carries the scroll cams.

In this manner both the Vernier and coarse switching assemblies are driven from a common drive shaft and drive source. With reference to FIG. 1, rotation of drive shaft assembly 254 is imparted to the drive train of both the coarse and Vernier switching assemblies. As illustrated, initially the Geneva drive for the coarse switching assembly is moved simultaneously with the Vernier drive. Simultaneous movement continues until both Geneva pinions are free of the Geneva gears whereupon the Vernier switching assembly continues to step while the coarse is held at its established setting. This operational condition continues until the Geneva pinions re-engage the Geneva gears whereupon the coarse setting is -changed with the Geneva drive eventually again being interrupted to leave the coarse switching assembly at a new setting while the Vernier continues to operate. With the described drive arrangement, the coarse switching mechanism has a given range of movement, for example a complete revolution of the Geneva pinion, or pinions. During a portion of that range of movement, the movable switches of both the coarse and Vernier switching assemblies move simultaneously but for the remainder of the range of movement of the coarse switching assemblies only the movable switches of the Vernier switching assemblies move. Accordingly, a coarse tap setting or Voltage can be established through the coarse switching assembly and, after the selected setting is effected, the Vernier switching can continue to step to more precisely adjust the voltage, `all from a common drive source.

In the illustrated embodiment the drive unit 12 rotates drive shaft assembly 254 180 for each tap change. This rotation of the common drive shaft assembly is transmitted through miter gears 280 and 282 to the scroll cams, the gearing here is 1:1 so that the scroll cams rotate 180 during each tap change. Thus on each tap change one of the contact assemblies 56 or 88 is moved from one stationary contact to an adjacent stationary contact while the other movable contact is held in engagement with the preceding stationary contact. On the next 180 of rotation of the scroll cam, i.e. the next tap change, the other movable contact is moved Iso that both contact assemblies will engage the same stationary Contact, In this manner movable contacts 56 and 88 of the Vernier switching assemblies move sequentially from one contact to an adjacent stationary contact.

The stationary contacts of the coarse and Vernier switching assemblies have been labeled in accordance with their corresponding tap connection, i.e. N and 2-9 in the Vernier arrangement and A-H and I in the coarse. The switching assemblies, movable contacts and Geneva pinions are illustrated in a recommended initial setting, both movable Vernier contacts on contact 6, movable coarse contact on contact A, movable coarse contact 190 between contacts A and J, Geneva pinion 210 on the Vertical centerline and Geneva pinion 208 angularly spaced 40 from Geneva pinion 210 in a clockwise direction. This initial position is desired as it establishes a base setting of the movable coarse -contacts from which adjustment can proceed. As a result of reduction gearing achieved in gears 276 and 278 and gears 250 and 240 (3:1 reduction at each set of gears), the Geneva pinions rotate 20 fol each tap change so that for each of rotation of drive shaft assembly 254 the Geneva pinions rotate 20. Remembering that Geneva pinion 208 controls movable contact 140 and pinion 210 controls movable contact 190, initial tap change movement of the drive system rotates the Geneva pinions 20 (in a -clockwise direction) to move pinion 20S free of its gear and in doing displaces movable Contact 140 slightly in a counterclockwise direction but maintains engagement thereof on contact A. Because of the relationship between the Geneva pinions and their respective gears, when the gears and movable coarse contacts are driven a full step by the pinions they move approximately 10 for each 20 of movement of the Geneva pinions. Thus, simultaneously with the slight movement of contact 140 contact 190 is moved a full step, approximately 10, to dotted line position No. 1 (see FIG. 8) onto stationary contact A. During this initial tap change the scroll cam is operated to step movable contact 88 from stationary contact `6 to 7 leaving movable contact 56 at contact 6.

Assuming continued tap changes in the same direction, on the next tap change movable contact 140 remains stationary (its Geneva pinion now rotating free of its Geneva gear but pinion stop portion 220 engaging the Geneva gear to hold movable contact 140 in place) and movable contact is again driven a full `step moving to a position No. 2 on contact A with only a slight angular spacing between it and movable contact 140. In the Vernier switching assembly movable contact 56 is stepped to contact 7 so that both movable Vernier contacts engage contact 7.

On the next, or third step from the starting point, pinion 210 4moves free of gear 198 and in so doing displaces movable contact 190 slightly to bring it into alignment with contact 140 `which remains stationary. At this time movable Vernier contact 88 is moved to contact 8 so that in the Vernier switching assembly stationary contacts 7 and 8 are bridged. At this point the coarse setting is established with the Vernier winding being connected to tap A in the coarse Winding. The Vernier switching assembly will now operate alone moving the contacts thereof sequentially through engagement with the stationary contacts.

With the gearing and angular relationship in the illustrated embodiment, l0 additional tap changes occur before Geneva pinion 208 re-engages Geneva gear 172, the Geneva stop surfaces 220 and 232 having been in engagement with their respective gear teeth throughout this Vernier movement to hold the movable course contacts stationary. Upon re-engagement of pinion 208 in gear 172, movable contact 140 is displaced slightly. At this point the movable Vernier contacts are ibridging between stationary contacts 3 and 4. Upon the next tap change (Le. the l4th step from the initial setting) movable coarse contact 140 is displaced a full step to position No. 4 on stationary contact A but remains in engagement therewith, in the Vernier switch assembly movable contact 56 is stepped to conta-ct 4 bringing both movable Vernier contacts onto the same stationary contact. The next tap change moves contact 140 a full step to position No. off of contact A between A and B, on this step pinion 210 re-engages its gear 198 displacing movable contact slightly on contact A and movable Vernier contact 88 is moved from contact 4 to 5. Upon the next tap change both movable coarse contacts 140 and 190 each move a full step, 140 moving onto contact B to position No. 6 and 190 moving on contact A to position No. 4; movable coarse contact 5-6 follows 88 onto contact 5. In the next step both movable coarse contacts are again displaced a full step moving 140 to position No. 7 approximately on the centerline of contact B and moving 190 olf of A into position No. 5 between A and B; movable Vernier contact 88 has moved from -contact 5 to contact 6. On the next tap change pinion 208 disengages from gear 172 displacing coarse contact 140 to a point generally on the centerline of contact B, and maintaining it in engagement with contact B, contact 190 moves a full step to position No. 6 in contact with B; Vernier contact 56 moves from 5 to 6. On the following tap change Contact 190 moves another full step to position No. 7 adjacent contact 140, which has remained stationary, and Vernier contact 88 moves onto contact 7. Geneva pinion 210 leaves the Geneva gear on the next step and in so doing displaces movable coarse contact 190 slightly to bring it into alignment with contact 140. At this point a relatively permanent coarse setting is established and the Vernier switching assembly is again free to continue stepping within that setting and without disturbing the coarse setting, i.e. until the pinions reengage their Geneva pinions. This operation of establishing a coarse setting and without that setting providing Vernier adjustment continues through the full range of coarse adjustment. It is believed that having described operation from an initial setting through a full coarse adjustment -sufiicient explanation has been provided to permit following the remaining operation through the full range of coarse adjustment. The operation merely repeats itself and with illustrated arrangements each complete range of movement of the Geneva drives moves both movable coarse contacts from engagement on one stationary contact to engagement on a succeeding stationary contact. It will be noted that from the initial setting the movable coarse contacts are moved -to a point generally on the centerline of contact A, in subsequent movement through a complete Geneva cycle the contacts are each stepped in four approximately 10 increments so that they move to the centerline of a succeeding contact. It should be noted that the angular spacing and movement of the movable coarse contacts and the number and positioning of the stationary coarse contacts can be varied without departing from the spirit or scope of this invention, for example bridging as Well as symmetrical engagement of the movable coarse contacts on the stationary contacts could be provided to increase the range of available adjustment.

It will be appreciated that the load tap changer of this invention is not limited an any specific type of drive source so long as it produces the movement of the drive shaft assembly 254 discussed above. The drive source illustrated in the drawings includes a reversible motor 290 of suitable construction, for example a 11S-volt AC reversible motor. Output shaft 291 of the output drive assembly 252 receives its driven movement from a combination of miter gears 292 and 294. The miter gears are driven by Geneva gear 296, connected to miter gear 294, and Geneva pinion and stop 298. Drive movement is transmitted from motor 290 to Geneva pinion 298 through a spur gear reduction, spur gear 300 being driven from the motor and connected through idler gears 302, 303, and 304 which are connected to a common shaft 306 with Geneva pinion 298. Geneva gear 296 has six teeth and for each tap change the motor drives Geneva pinion 298 through three complete revolutions thereby imparting of rotation to shaft 252 in three increments.

One of the advantages of the drive arrangement is its adaptability to hand cranking. As shown, shaft 306, which supports Geneva pinion 298, can be provided with an extension 308 exposed exteriorly of the drive housing. Extension 308 is adapted to receive a hand crank 309 to permit manual cranking of the tap changer through its various steps for inspection and testing and also to permit initial positioning of the tap changer elements as described above. An on position indication 310 is associated with the output shaft to be used as an indication during hand cranking.

The drive assembly includes an indicator 312 and limit switches 314 which operate in a conventional manner. The limit switches set the extremes of control for the tap changer whereas the indicator gives a Visual read-out of the position of the tap changing mechanism. The drive train for the indicator and the cams for operating the limit switches can take any conventional form. As illustrated, the stepped motion of Geneva gear 326 is transmitted through a set of miter gears 328 and 330 to shaft assembly 332. The shaft assembly includes worm 334 which meshes with pinion 336 -to drive the shaft for the indicator means and also the shaft carrying the cams (not shown) for operating the limit switches.

The tap changer of this invention provides a relatively simple and effective arrangement for achieving precise voltage adjustment through the use of coarse and Vernier switching assemblies. The common drive source for both switching assemblies permits relatively simple synchronization of the switching assemblies. Furthermore, it will be noted that the coarse switching assemblies are not subjected to any arcing, all arcing occurring in the Vernier assembly.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modiiications may be made therein Without departing from the spirit of the invention or from the scope of the appended claims.

I claim:

1. Electrical tap changing mechanism comprising, in combination,

first switch means inolu-din-g first movable contact means,

a Iplurality of first stationary contact means positioned in the path of movement of said first movable contact means and means supporting said first movable contact means for sequential engagement with said first stationary contact means,

second switch means comprising a `plurality of second stationary contact means, second movable contact means supported for sequential engagement with said Second stationary contact means, and motion transmitting means having a range of movement and connected to said second movable contact means and operative to move said second movable contact means into sequential engagement with said second stationary contact means, said motion transmitting means having a driving connection with said second movable contact means only for a first portion of said range of movement and moving yrelative to said second movable contact means for a second portion of said range of movement,

drive means having drive connections to said first movable contact means and said motion transmitting means, said drive means operative to simultaneously drive said first movable contact means through sequential engagement with said first stationary contact means and said motion transmitting means through said range of movement so that during said first portion of said range of movement said first and second movable contact means move together and during said secon-d iportion of said range of movement said second movable contact means remains at rest 1 1 in the position assumed at the end of said first portion of said range of movement While said first movable contact means can continue movement.

said motion t-ransmitting means including Geneva `gear means having a ldriving connection to said second movable contact means, Geneva pinion and stop means for driving said Geneva gear means, sai-d Geneva pinion means having a driving connection with said Geneva gear means for a portion of the movement thereof and said Geneva stop means having holding engagement With said Geneva gear means for the remainder of the movement thereof,

and means connecting said drive means to said Geneva pinion and stop means.

2. The tap changing mechanism of claim 1 wherein said first movable contact means has a repeating sequence of engagement with said first stationary contact means when continuously driven by said drive means,

said drive and stop engagement of said pinion and stofp means with said Geneva gear means occurs sequentially and wherein said drive engagement portion is less than a sequence of said first Amovable contact means and during at least a portion of the remainder of said sequence said second movable contact means is at rest.

3. The tap changing mechanism of claim 1 wherein said second stationary contact means includes first and second sets of stationary contacts and said second movable contact means includes first and second movable contacts for sequentially engaging the stationary contacts of said first and second sets respectively,

said Geneva gear means includes first and second Geneva gea-rs connected one to each of said first and second movable contacts and said Geneva pinion and stop means includes Geneva pinion and stops for each of said first and second Geneva gears,

and wherein said Geneva pinion and stops for said first and second Geneva gears are angularly `offset `from each Aother to sequentially move said movable contacts with respect to said first and second stationary contacts.

4. The tap changing mechanism of claim 2 lwherein said drive means includes common motor means and drive connections from said motor means to said first movable contact means and said motion transmitting means.

5. Electrical tap changing mechanism comprising, in combination,

first switch means including first movable contact means,

a plurality of first stationary Contact means positioned in the path of movement of said first movable contact means and means supporting said first movable contact means lfor sequential engagement with said first stationary contact means,

second switch means comprising a plurality of second stationary contact means, second movable contact means supported for sequential engagement with said second stationary contact means, and motion transmitting means having a range of movement and connected to said second movable contact means and operative to move said second movable contact means into sequential engagement with said second stationary contact means, said motion transmitting means having a driving connection with said second movable contact means only for a first portion of said range of movement and moving relative to said second movable contact means for a second portion of said lrange of movement,

drive means having drive connections to said first movable conta-ct 4means and said motion transmitting means, said drive means operative to simultaneously drive said first movable contact means through sequential engagement with said first stationary contact means and said motion transmitting means through said range of movement so that during said first portion of said range of movement said first and second movable contact means move together and during said second portion of said range of movement said second movable contact means remains at rest in the position assumed at the end of said first portion of said range of movement while said first movable contact means can continue movement,

and said first and second switch means being operatively connected to tapped windings and cooperating in providing tap changes with the tap changes affected by said second switch means being greater than that of said first switch means so that said second switch means provides coarse tap change adjustment and said first switch mean provides Vernier tap change adjustment.

6. The tap changing mechanism of claim 5 wherein said motion transmitting means includes means mechanically holding said second mov-able switch means in said rest position during said second portion of said range of movement.

7. Electrical tap changing mechanism comprising, in

combination,

first switch means including first movable contact means,

a plurality of first stationary contact means positioned in the path of movement of said first movable contact means and means supporting said first movable contact means for sequential engagement with said first stationary contact means,

second switch means comprising a plurality of second stationary contact means, second movable contact means supported for sequential engagement with said second stationary contact means, and motion transmitting means having a range of movement and connected to said second movable contact means and operative to move said second movable contact means into sequential engagement with said second stationary contact means, said motion transmitting means having a driving connection with said second movable contact means only for a first portion of said range of movement and moving relative to said second movable contact means for a second portion of said range of movement,

and drive means including common motor means having drive connections to said first movable contact means and said motion transmitting means, said drive means operative to simultaneously drive said rst movable contact means through sequential engagement with said first stationary contact means and said motion transmitting means through said range of movement so that during said first portion of said range of movement said first and second movable contact means move together and during said second portion of said range of movement said second movable contact means remains -at rest in the position assumed at the end of said first portion of said range of movement while said first movable Contact means can continue movement.

8. Electrical t-ap changing mechanism comprising, in

combination,

first switch means including first movable contact means, a plurality of first stationary contact means positioned in the path of movement of said first movable contact means and means supporting said first movable contact means for sequential engagement with said first stationary contact means,

a plurality of first tap connections connected to said first stationary contact means,

second switch means comprising -a plurality of second stationary contact means, second movable contact means supported for sequential engagement with said second stationary contact means, and means supporting said second movable contact means for sequential engagement with said second stationary contact means,

a plurality of second tap connections connected to said second stationary contact means,

and drive means connected to and operative to drive said first and second movable contact means through sequential engagement with said first and second stationary contact means, said drive means having a range of movement and operative during a first portion of said range of movement to drive said first and second movable contact means and during said second portion of said range of movement driving only said first movable contact means with said second movable contact means remaining at rest in the position assumed at the end of said rst portion of said range of movement while said first movable contact means can continue movement,

the tap changes affected by said second switch means being greater than that of said first switch means so that said second switch means provides coarse tap change adjustment and said first switch means provides Vernier tap change adjustment.

9. Tap changing mechanism comprising, in combination,

drive means,

coarse winding means including a plurality of tap connections therein,

coarse switching means including a plurality of coarse stationary contact means connected to said coarse winding means tap connections and movable coarse contact means supported for selective movement into engagement with said coarse stationary contact means,

motion transmitting means connected to said coarse movable contact means -and `said drive means for transmitting motion from said drive means to said coarse movable contact means, said motion transmitting means having -an operative range of movement and characterized by providing a driving connection between said drive means and said coarse movable contact means for a first portion of said operative range and providing relative movement between said drive means and said coarse movable conaaaaals tact means for a second portion of said operative range,

Vernier winding means connected to said coarse switching means and including a plurality of tap connections therein,

Vernier switching means including a plurality of Vernier stationary Contact means connected to said Vernier winding means tap connections and movable Vernier contact means supported for relative movement into engagement with said Vernier stationary contact means,

Iand means connecting said drive means to said movable Vernier contact means to drive said movable Vernier contact means relative to said Vernier stationary contact means so that said coarse and Vernier switch means are both driven from said drive means with said coarse and Vernier movable contacts moving jointly during said first portion of said operative range and during said second portion of said operative range said coarse movable contact means remains stationary as said Vernier movable contact means can continue motion.

10. The tap changing mechanism of claim 9 wherein said Vernier switching means has a repeating sequence of engagement of said Vernier movable contact means with said Vernier stationary contact means when continuously driven by said drive means,

and the portion of said operative range during which said motion transmitting means provides a driving connection to said movable coarse contacts is less than said sequence and during at least a portion of the remainder of said sequence said movable coarse contact means is at rest.

References Cited UNITED STATES PATENTS 5/1966 Bleibtreu et al. 200-18 LEWIS H. MYERS, Primary Examiner'.

I. R. SCOTT, Assistant Examiner. 

